Wagner thought Jones 'was going mad'

One of the brothers suing Alan Jones for $4.8 million in defamation thought the broadcaster was going mad when he accused the Wagner family of being responsible for 12 deaths in the 2011 Queensland floods.

Neil Wagner is giving evidence in Brisbane Supreme Court, where he and brothers Denis, John and Joe are suing the talkback host, Harbour Radio, 4BC and journalist Nick Cater.

The Wagners say Jones accused them of being responsible for 12 deaths at Grantham during the 2011 floods, when one of the walls of the Lockyer Valley quarry they owned collapsed.

During an emotional session in the witness box Neil Wagner broke down several times as he was questioned about the effect of Jones' comments on his family during 32 broadcasts in 2014 and 2015 .

"I thought this bloke was going mad, senile," he said.

But as the alleged defamation continued, it began to have a negative effect on their reputation in the community, he told the court.